29) ice cream melting.
A physical change is the change where the material that make up the thing itself never change. Unlike chemical change where the materials making up things change like in chemical reactions, you start with water and salt you end up with an acid!
30) metals and nonmetals.
To the left of the periodic table you can find the metals, to the right you can see nonmetals. At the middle you can fin metalloids and other elements.
31) sound.
Sound waves are mechanical waves that need media to transport.
Hope this helps.